1. Field of the Invention
The present invention relates to a displacement sensing circuit for sensing a displacement of a measured magnetic object by sensing a change in inductance of detecting coils, and being capable of sensing such a displacement without being influenced by external noises caused by interference signals even though these noises are picked up by the detecting coils and the wires interconnecting the coils and electric circuits.
2. Prior Art
FIG. 1 shows the construction of a displacement sensing system of the prior art. In this figure, a pair of displacement sensors A and B are disposed on an axis X passing the center of a rotor (a measured object) P made of magnetic material, and another pair of displacement sensors C and D are disposed on an axis Y perpendicular to the axis X and passing the center of the rotor P. Each of the displacement sensors comprises a magnetic core and a detecting coil wound around the magnetic core. Detecting coils A-1 and B-1 of the displacement sensors A and B, respectively, disposed on the axis X are connected in series and serve to detect a displacement of the rotor P along the axis X. Detecting coils C-1 and D-1 of the displacement sensors C and D, respectively, disposed on the axis Y are connected in series and serve to sense a recurring displacement of the rotor P along the axis Y. This detection utilizes such a characteristic that the inductance of the detecting coils changes due to the displacement of the rotor P from a predetermined position with respect to the detecting coils.
When such a displacement sensing system is used in a circumstance where interference noise arises, the detecting coils, electric circuits connected to the coils and the wires interconnecting them pick up such noise signals which are superimposed on the output signals of the detecting coils, that is, displacement signals amplitude-modulated by the displacement of the rotor P, which causes the displacement signals to be distorted by the noise and the accuracy in sensing the displacement of the rotor to deteriorate.